JAVA is an object oriented programming language that has become a de facto standard in network programming. At the present time, JAVA is also beginning to be utilized in the domain of embedded systems, or systems that contain a microprocessor or a microcontroller. Some of the strong points of the JAVA environment like its object orientation, automatic garbage collection and run time security features can be used with success in embedded applications. However, its run time environment presents a challenge for system designers because of the resource overhead related to running the JAVA code in a virtual machine such as an interpreter or a just-in-time compiler. The JAVA binary code, called bytecode, is distributed in one or more class files. Bytecodes are the instructions of a hypothetical computer that is specifically designed for the execution of JAVA programs. Conventional CPUs cannot execute this bytecode and therefore execute it in a software layer called the JAVA Virtual machine. This machine is an abstract machine specification and no implementation guidelines are given. The JAVA Virtual Machine Specification is published by Sun Microsystems.
With reference to FIG. 17, there are basically four ways to execute a JAVA program on a physical computer platform. In a first method 902, the opcode is computed in a JAVA compiler 915 and the JAVA bytecode 925 is sent to an interpreter 930 before being sent to the operating system 950 and being executed by the CPU 960. However, the interpreter 930 presents a speed penalty of a factor of five compared to executing a program compiled to native code.
A second method 903, is similar except that instead of using an interpreter, the JAVA bytecode is dynamically compiled into the binary format 940 for the native platform by a Just In Time (JIT) compiler 935. This process occurs inside the virtual machine and is not stored after the program has ended. The newest JAVA JIT technique is called HotSpot and uses a principle where bottlenecks are analyzed and recompiled during program execution. However, the JIT compiler will suffer from a memory overhead of a factor of two or three while executing the same application.
A third method 901 involves the use of cross compilers 910 to compile the JAVA source code into binary format 920 for the native platform. However, the platform independence is lost and the binary program cannot be executed on multiple platforms.
In a fourth method 904, a JAVA operating system 945 and JAVA processor 970 are used to execute the bytecode directly silicon. Some JAVA processors have a folding mechanism, which means that several instructions are combined and executed as one. However, most JAVA processors will execute as an interpreter wherein each opcode is read and then the appropriate action is taken to execute the instruction.
There is no generally preferred run-time environment. Each of these environments can be used with success for different systems depending on their requirements. However, for embedded systems, the use of a JAVA processor (the fourth method 904) is by far the preferred technical solution if JAVA is to be implemented in embedded systems. In recent years, several JAVA virtual machines have been developed for embedded processor platforms. Most of the software solutions aim for 32 bit processors with some 100K memory size. Additionally, some JAVA hardware processors for executing JAVA programs on silicon have also been developed. These processors, which support direct execution of JAVA instructions, implement 32 bits stack machines. Some rely on extensions to the JAVA binary format in order to offer features like direct addressing and bit manipulation instructions. Others do not execute JAVA binary codes directly, but have a very close architectural match to thereby increase performance of the virtual machine. The processors are all targeted for medium to large embedded systems. There are currently no 8 or 16 bit processors available for direct execution of JAVA byte compiled code, even though the eight bit processor market has been considerably larger than the 32 bit processor market.
It is the object of the present invention to provide a microprocessor for executing JAVA byte compiled code in hardware.
It is a further object of the present invention to provide a microprocessor architecture for executing JAVA that is small and power efficient enough to be a preferred solution in small to medium sized embedded applications.